Why you should let fallen antlers lie: they’re still in use

Published: November 20, 2019

Fallen antlers against a wooden background Photo by stockcreations/Shutterstock

As the holiday season approaches, it’s tempting to collect fallen antlers from the wild to use in rustic winter decorations. But after a deer or moose is done with them, antlers still have a lot to contribute.

Do you consider yourself a homebody? You’ve got nothing on the antler fly, a species whose males can spend their entire adult life on a single shed antler of a moose or deer. Antler flies typically live for about a week as adults, a month at most. While that doesn’t make for much of an exciting life by our standards, it does make them excellent subjects for researchers to study the science of aging.

“For a long time we didn’t think insects aged,” says Christopher Angell, a Ph.D. candidate in biology at the University of Ottawa who studies antler flies in Algonquin Provincial Park. While insects had been observed deteriorating under lab conditions as they got older, Angell says that “we figured that was such a slow process, and insects tend to live such short, perilous lives in the wild, that it really wasn’t a consideration for wild insects.” That all changed in 2002, when Russell Bonduriansky, a researcher at the University of Toronto, showed that the longer antler flies were alive, the less likely they were to mate and survive.

One reason antler flies make good study candidates for aging research is that they tend to stay in one place throughout their adult life. Their survival entirely centres around antlers. Moose and deer shed their antlers in wintertime, and come spring, adult antler flies congregate on the bones. Males fight to stake out a territory roughly the size of a toonie, but that can drop to the size of a quarter on the most attractive antlers.

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Female antler flies fly from antler to antler to find the best mates. After a female chooses a male and completes a two-hour mating process, it lays eggs directly into the antler’s spongy bone matrix. The eggs hatch into larvae that feed on bone marrow for about a month and a half to two months. Once they reach a centimetre in size, the larvae are ready to pupate, but they wait inside the antler for the signal that it’s time to go: rainfall.

When an antler fly larvae hears the sound of rain and feels moisture seeping into the antler, they start moving. “They climb out of the cracks and pores in the antler onto the surface,” says Angell. The larvae then “climb to the tips of the antler prongs, form themselves into a little loop, tighten all their muscles and then suddenly straighten out, releasing all that tension and flinging themselves through the air.” The larvae can hurl themselves up to half a metre in a single jump. After landing, they may jump a couple more times before burying themselves in the leaf litter to pupate for about two weeks. They then emerge as adult flies and the whole process starts again, says Angell.

For his research, Angell collects antler flies so that he can observe them over the course of their whole lives. In dry periods without rain, Angell has to trick larvae into thinking it’s raining so that they climb to the surface of their moose antler homes. “I take my moose antlers and set them out on a table and spray them with water,” says Angell. He then takes “whatever’s around, whether that’s sticks or pens, and just drum on them to mimic the sound of raindrops hitting.” Not all of the antler flies are convinced, adds Angell, but he’s able to successfully lure enough larvae to the surface for his research.

To keep track of his study subjects, Angell trims a paintbrush down to three or four bristles, then writes letters and numbers on the backs of the two-millimetre-long antler flies. This allows him to identify and follow individuals throughout their adult lives.

One aspect of aging that Angell looks at is the probability that a fly will survive or die as it gets older. “If it’s very rare to die at three days, but very common to die at seven, then that tells you there’s some sort of increase through their life in the probability of dying,” says Angell. He also records male mating success, and where the flies are located on the antler in relation to their age.

Angell thinks its important to study aging in natural populations because in a laboratory setting “there’s never any stress, there’s always enough food, there’s never any danger, and there’s never bad weather.” He adds: “That’s not really how people or other animals live their lives.”

As the holiday season approaches, it’s tempting to collect fallen antlers from the wild to use in rustic winter decorations. However, in addition to shed antlers being habitat for antler flies, Angell says they are used by a variety of insects as a display platform to attract a mate. Mammals will chew on antlers during the winter for a calcium boost, and rodents and rabbits, animals with ever growing teeth, gnaw on antlers to keep their teeth worn down. Because antlers are used by a variety of wildlife, Angell suggests it’s best to leave them be.

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